Plant Leaf Holes: Typical Causes and Remedies

In the horticultural world, holes in plant leaves can be a common sight, and understanding their causes is essential for effective garden management. From insects to diseases, various factors can contribute to this issue.

One of the most common leaf-damaging insects in Germany is the caterpillar, particularly the larvae of May and June beetles known as Engerlinge. While they mainly damage roots, other insects like beetles, earwigs, grasshoppers, and caterpillars themselves cause visible leaf damage. For instance, Japanese beetles feed between leaf veins, leaving a lacy or skeletonized appearance on the leaves.

Whiteflies, tiny, white-winged insects that feed in groups, are another culprit. They flutter up when disturbed and leave a sticky residue that attracts ants and also promotes the growth of sooty mold. Aphids, too, leave a sticky residue and can attract ants.

Insecticidal soap, Neem oil, or other horticultural oils can be effective against soft-bodied insects such as aphids or whiteflies. For more persistent pests like beetles or caterpillars, Bacillus thuringiensis (Bt) and neem oil (azadarachtin) may prove beneficial.

Fungal diseases can also create spots and holes in leaves. Shot-hole disease, caused by a bacterium-fungus, can cause holes in leaves, particularly on fruit trees and ornamental cherry trees. Healthy trees generally can tolerate shot-hole disease, so no intervention is needed, other than picking up and removing dead leaves.

Leaf miners, fly larvae that feed on the inside of leaves, cause tan blotches that wind across a leaf. Slugs, not insects but members of the mollusk family, leave shiny trails across leaves that sparkle in the sun and damage plants by clipping off plant parts or creating smooth-edged holes in leaves or in maturing vegetable fruits that touch the ground.

Slugs favor shady areas and feed on low-lying vegetation and decaying matter. To control slug populations, consider using barriers, traps, or baits.

Grasshoppers feed on leaves, stems, flowers, fruits, and seed heads, leaving irregular holes within the leaf or on leaf edges. Squash bugs lay bronze-colored eggs in clusters on leaves.

Vigilance in the garden is important for early detection of potential pests or diseases. By assessing the size and shape of the holes, and looking for tunnels, slime, or insects on the leaves or stems, gardeners can take prompt action to protect their plants.